The invention relates to a method for redeveloping or renovating sewer conduits and sewer ducts. Redeveloping or renovating are measures for improving the present performance of sewer drains and sewer ducts, the original substance being completely or partly included. In the following only the redeveloping of sewer drains is described, including, however, the redeveloping as well as the renovating of sewer drains as well as sewer ducts.
Sewer drains have to be redeveloped from time to time because the sewer drains are subject to environmental influences and, after a certain time, cannot meet the wanted requirement anymore, for example due to leakage.
In Germany, for example, sewer ducts of a length of several hundreds of thousands of kilometers have to be redeveloped in the near future. In Germany there are approximately 1,400,000 km sewer ducts. Approximately 750,000 km have to be redeveloped. According to calculations this will cost up to 150 billions (150xc3x97109) deutschmarks during the next years.
Today, plastic tubes (for example of polypropylene) are used for redeveloping sewer ducts. Several different lining methods are used. One method group of the lining methods is the so called tube relining, with which self-supporting plastic tubes are introduced as sections into the sewer pipes to be redeveloped in order to restore or improve the resistance to physical, chemical, biochemical and/or biological corrosion for preventing the new formation of incrustations, for restoring and/or improving the static load capacity and the water tightness. Thereby, the dimensions of cross section of the sewer pipes to be redeveloped or of the access pits are reduced.
The relining methods can be distinguished into piping relining, long-tube relining and section is inserted in one single operating cycle into the section of the sewer pipe to be redeveloped. An annular space is formed between the plastic piping constituting the xe2x80x9cinlinerxe2x80x9d and the sewer pipe to be redeveloped. This annular space is filled by a filling material. For example sands, free-flowing hydraulically bondable materials and foaming masses are used as filling material. The method is independent of the cross-sectional shape of the sewer pipe. As a rule, circular cross sections in the nominal value range of DN 80-DN 2000 with lengths up to 700 m are redeveloped depending on the condition of the line of the mounting. In contrast to the piping relining, during long-tube relining and short-tube relining self-supporting single tubes are introduced discontinuously into the sewer pipes to be redeveloped. Also these methods can be adapted to the different shapes of cross-section of the sewer pipes. The redeveloping method to be used depends on the local conditions.
The redeveloping of sewer ducts is subject to several problems. On one hand, it is very expensive and, on the other hand, environmental problems arise because ecological damages occur.
A further environmental problem is the sanitation of scrap rubber, in particular of used vehicle tires. In order to prevent environmental pollution, during the last years there have been made a lot of efforts to reutilize such old tires and to make use of the valuable energy source.
The raw material utilization of old tires is concentrated on different methods of pyrolysis, hydrogenation and gasification. The products resulting thereby (oils, gases, coke, soot. etc.) normally have to be purified before utilization and are expensive. The raw material utilization furthermore sets free pollutants and has to be combined with expensive method steps for sewage clarification and exhaust gas clarification.
Today, the energetic utilization of old tires comprises the controlled combustion of old tires in the cement industry. However, there are already capacity bottlenecks.
Furthermore, stability problems in the production process of the cement production occur when the feeding rate is high.
The importance of dumping of old tires decreases more and more due to the fact that the costs of the dumping ground rises. Further problems are the potential fire risk, the spontaneous pyrolysis and the risk of affect of parasites.
Furthermore, there is a need of action in the field of sanitation of old tires because of criminal dispose of old tires which occur more often.
Several methods are known for reutilization of scrap rubber, in particular old tires.
EP-PS 0 493 732 discloses a method for preparation of sulfurous scrap rubber. The rubber is comminuted to ground rubber. Then, from the comminuted rubber, reclaimed rubber is generated by devulcanization. The comminuted rubber is held in a bacterial suspension of chemolithotropic microorganisms during supply of air until the sulfur is separated as elementary sulfur and/or sulfuric acid partly or completely from the remaining replastified reclaimed rubber. The reclaimed rubber thus replastified is reused in certain portions of weight in the t read mixture when retreading old tires.
DE-OS 44 31 336 discloses material compositions which contain a mixture of pulverized old tires, one or several resinous substances and chemical reagents. The resinous substances are chosen from polypropylene resin, polyethylene resin of low density and polyethylene resin of high density. The chemical reagents are chosen from the group of acetone, coustic soda, glass wool, ammonium phosphate, starch and pigments. In order to fabricate structural products from these-material compositions, the components are mixed together, the mixture is melted at 230 to 350xc2x0 C. an d the mixture is drawn by means of a rotational molding method, extrusion method or press-form method. When producing sewer pipes according to this method, the material composition comprises pulverized old tires and resinous substances as well as acetone, glass wool, ammonium phosphate and/or starch. The additions acetone, glass wool, ammonium phosphate and/or starch serve, for example, to improve the inherent stability of the sewer pipes.
DE-OS 44 33 961 discloses a method for fabricating structural products and flat articles from a recycling mixture on the basis of ground rubber and polyethylene. The polyethylene is melted and kneaded. The ground rubber and possibly additional substances are added. The polyethylene mixture is then kneaded by a roller.
DE-OS 42 20 623 discloses a method for fabricating fine-grained rubber powder from vulcanized old tires, the produced rubber powder compounded with recycled thermoplastics of the same fineness being able to be processed to a new raw material.
It is the object of the invention to provide a favorable method for redeveloping sewer ducts.
According to the invention this object is achieved by
(a) producing a tube of low inherent stability from scrap rubber and plastic material, and
(b) introducing this tube into an old sewer pipe of the sewer ducts, the tube of low inherent stability being supported by the wall of the old sewer pipe.
In this context, tubes of low inherent stability means tubes which cannot withstand the load exposed to a sewer pipe. Such loads are, in particular, the pressure exerted by the soil.
The invention is based on the realization that the inherent stability of tubes used for redeveloping sewer ducts does not have to be very high when they are introduced into old sewer pipes of the sewer ducts already present. Then, these tubes of low inherent stability can be supported by the walls of the old sewer pipes and by the annulus filling.
Thus, a particular advantage of the method according to the invention is that the tubes can be fabricated exclusively from scrap rubber and plastic material. Because high inherent stability is not required, there is no need for normally used additional substances for increasing the inherent stability.
Due to the method according to the invention, the costs for redeveloping sewer ducts can be kept small, because the production costs for tubes constructed from scrap rubber and plastic material are lower than for tubes of pure plastic material (polypropylene) usually used.
The plastic material used for producing the tube can, for example, be polyethylene or polypropylene and fresh as well as recycled plastic material can be used. The scrap rubber used for producing the tube can be obtained from various scrap rubber sources. It can, for example, be functionalized EPDM (ethylene-propylene-diene-terpolymer).
Preferably, the scrap rubber used for producing the tube is processed to ground fine-grain rubber having a grain size of  less than 1 mm. This achieves a good miscibility with the plastic material. However, also certain additives can be used by means of which the miscibility of the scrap rubber and the plastic material is improved. Such additives are, for example, slip additives as crystalline polypropylene waxes having a molecular weight of about 2000.
When producing the tube the proportion of the ingredients scrap rubber and plastic material can be chosen variously. It has been shown to be particular favorable to use 50 to 70 percent in weight of scrap rubber and 30 to 50 percent in weight of plastic material.
As explained above, old tires can be used for producing the tube of low inherent stability. Thus, the method according to the invention also solves important environmental problems, because a very large amount of old tires can be used. The amount of old tires in Germany is approximately 600,000,000 kg per year. It can be shown that all of the old tires obtained during a time period of about 12 years can be used up when redeveloping the sewer ducts using the method according to the invention. This number is achieved by assuming that the share of scrap rubber (including soot and filling material) in old tires is approximately 70%. This results in an amount of scrap rubber of 420,000,000 kg per year. With an approximate density of the scrap rubber of 0.93 g/cm3, the volume of scrap rubber is calculated to be 450,000 m3. With an average cross-section of a sewer duct of DN 500 (500 mm) the circumference is 1.57 m. With a redeveloping requirement of 750,000 km sewer ducts, this results in a surface of approximately 1,200,000,000 m2. With a thickness of the layer (corresponding to the wall thickness of the tube) of 6 mm this results in a volume of 7,200,000 m3. When 70% of the used material is scrap rubber, this results in a volume of 5,100,000 m3 to be filled by scrap rubber. Thus, the method according to the invention supplies a long-term solution for elimination of old tires, the life-cycle costs for the sanitation of old tires being saved.
When producing the tubes of old tires using the method according to the invention it can be proceeded as follows:
First the old tires are sorted according to rubber quality, shredded, granulated, ground and made free from foreign substances (steel, textural nylon etc.). The grinding can be effected in the form of warm grinding as well as cold grinding (cryogen grinding). The individual process steps are known per se.
Apart from untreated ground rubber also particularly treated ground rubber can be used. This ground rubber can be produced according to one of the known methods for producing ground rubber, for example according to the method described in EP-PS 0 493 732. The surface modified ground scrap rubber produced by means of this method is, in connection with plastic material (for example polypropylene or polyethylene) well suitable for producing plastic products.
The plastic material, for example polypropylene, used for producing the tubes using the method according to the invention is mixed with the ground rubber likewise according to a prior art method, such that a raw mixture is created.
Now, from this raw mixture, tubes or structural parts are produced by extrusion, rotational molding or press production processes giving the tubes or structural parts a desired thickness, size and cross-sectional shape. The material properties of the thus produced tubes are set through the composition of the raw mixtures and the processing parameters. Such methods are known per se.
The tubes of low inherent stability produced by using the method according to the invention are then introduced into the old sewer pipes according to one of the above mentioned relining methods.
When the outer dimensions of the tube of low inherent stability are smaller than the inner dimensions of the old sewer pipe, such that a space is formed between the tube of low inherent stability and the old sewer pipe, the consumption of scrap rubber used in the method according to the invention can be increased further by filling this space by scrap rubber or by a material containing scrap rubber.
The cross-sectional shape of the used tubes of low inherent stability can be arbitrary. Advantageously, however, they are adapted to the cross-sectional shape of the old sewer pipe and can be circular.